Production processes in micro- and nano-technology requires adequate measuring instruments to obtain three-dimensional (3D) geometries. Vertical scanning interferometry (such as scanning white-light interferometry, in one example) achieves a nanometer resolution/accuracy in the axial direction, and is particularly suited for the measurement of step height structures (for example, in micro-electro-mechanical, MEMS, structures). The measurement principle is based on a so-called phase-shifting, or depth scan, or z-scan, during which the optical path difference between the measuring and reference arms of the interferometer is varied in small steps. In the situations where the field-of-view (FOV) subtended by the object/sample is substantially higher than the FOV of the optical objective used with the interferometer, or in situations where the dimensions of the sample are incomparably larger than the FOV of the optical objective, the usefulness of this approach is severely diminished, both due to impractically-long times required for profiling of the whole sample, the errors introduced at high numerical apertures, and the continuous need for cumbersome stitching of images.
The methodology of lateral scanning white-light interferometry, while allowing for a continuous data acquisition and substantially eliminating the need for image stitching, requires an angular tilt between the optical axis of the objective and the normal to the sample surface, leading to a critical need in a regular stage tilt calibration.